This invention relates generally to electronic energy consumption metering circuits, and more particularly to electronic metering circuits which employ switched-capacitor integrators and which may be fabricated on a single integrated circuit chip.
Electronic circuits for measuring electrical energy consumption in an electrical system, such as an AC power distribution system, are well known. Typically, these circuits may comprise a switched time division multiplier for multiplying two signals representative of the instantaneous current and voltage in the electrical system and for providing a product signal which is representative of the instantaneous power being supplied by the electrical system. The product signal from the multiplier may be integrated in an integrator circuit to provide a signal representative of the average power or energy consumption, and this signal may be converted to a pulse train in which each pulse represents a predetermined unit quantity of energy. The pulses may be counted or accumulated to provide a measure of total energy consumption. This basic technique of electronic metering is described, for example, in U.S. Pat. No. 3,955,138 which issued to the present inventor, and various electronic metering circuits employing this technique are disclosed in other patents of the present inventor, including U.S. Pat. Nos. 4,066,960; 4,217,546; 4,485,343; 4,495,463; and 4,535,287. The foregoing patents are all commonly assigned with the present invention to General Electric Company, and are incorporated by reference herein.
While the electronic circuits disclosed in the foregoing applications are capable of accurate metering and perform satisfactorily, it is desirable to provide electronic metering circuits which have improved accuracy, reduced cost and size, and which are capable of being fabricated entirely on a solid state semiconductor monolithic integrated circuit chip. In the past, electronic metering circuits have been fabricated, at least in part, on integrated circuit chips. It is relatively easy to fabricate components such as analogue switches, amplifiers, logic elements, etc. on silicon chips using, for example, MOS technology. Some difficulties have been encountered, however, in attempts to fabricate electronic metering circuits entirely on integrated circuit chips. For example, in order to afford the desired degree of metering accuracy, close matching and control of the values of some resistor and capacitor components are necessary, and this has generally required the use of precision components. It is very difficult to control characteristics such as value and temperature coefficient of integrated circuit resistors, and obtaining well-matched components in circuits such as R-C integrators where close matching is necessary for good accuracy has been practically impossible. Furthermore, MOS resistors have a low sheet resistance, and to obtain resistors having a large value requires a large chip area. Since it is easier to match the temperature and voltage coefficienss of integrated circuit capacitors and obtain a desired capacitance ratio, it has been proposed to replace the conventional R-C type of integrator of known electronic metering circuits with a switched-capacitor type integrator. The present inventor's commonly assigned copending application Ser. No. 812,369, filed Dec. 23, 1985, now U.S. Pat. No. 4,682,102 discloses an electronic metering circuit employing a switched-capacitor integrator that is capable of being fabricated on a single chip, which application is incorporated by reference herein. Although the electronic circuit of the copending application is quite satisfactory, the ratio of the capacitors in the switched-capacitor integrator is quite large. This has made it difficult to match the capacitors and has necessitated a relatively large chip area for fabrication. It is desirable to reduce the capacitor ratio in the switched-capacitor integrator of such electronic metering circuit in order to reduce the chip area and to improve the capacitor matching, and it is to this end that the present invention is directed.